Engine fuel feed device



April 21, 1959 c. REGGIQ 2,882,880

ENGINE FUEL FEED DEVICE Original Filed Nov. 4, 1943 United ENGINE FUELFEED DEVICE Ferdinando Carlo Reggio, Tampa, Fla.

3 Claims. (Cl. 123-119) This invention relates to fiuid flow regulatingsystems and more particularly to fuel metering and control systems forcombustion engines, this application being a division of applicantsco-pending application Serial No. 508,897 filed November 4, 1943, forFuel Supply System.

The invention is particularly adapted for aircraft propulsionpowerplants operating under varying conditions of barometric pressure,ambient temperature, thrust and speed.

An object of the invention is to provide an improved engine fuel controlwhich automatically and under all operating conditions whether steady ortransient maintains the ratio between engine fuel flow and engine airflow within predetermined upper and lower limits.

Another object is to provide an improved engine fuel control whichautomatically so regulates the fuel feed as to secure at all timesproper combustion mixtures and maintain the temperatures resulting fromcombustion within desired safe limits.

The above and other objects will be apparent as the descriptionproceeds. In the following description and in the claims various detailswill be identified by specific names for convenience, but they areintended to be as generic in the application as the art will permit.

The drawing, which shows an example of embodiment of the invention, is asectional elevational view of a fuel metering device anddiagrammatically indicates the connections thereof with the engine andthe fuel nozzle valves.

In the specific embodiment of the invention which is here described, theengine 80 is shown as an internal combustion engine provided with an airinduction system comprising a passage having an orifice or venturi 94therein, a valve 95 and an engine-driven compressor 99 delivering airunder pressure to a manifold 97 connected with the cylinder inlet portsleading to the combustion chambers.

The fuel system comprises an engine-driven fuel pump 47 which issupplied with liquid fuel at suitable pressure from a conduit 81 throughan orifice 82 whose effective area is controlled by a slide valve 83.The pump discharges fuel, always in excess of engine requirements, tothe supply manifolds 45.

A number of fuel injectors 9 are provided, each having an intake portconnected with one of the fuel supply manifolds 45, a nozzle valvethrough which fuel is delivered to the engine in quantity variable withthe fuel pressure, and a return port in free communication with theinlet port and connected with one of the return manifolds 39 throughwhich the excess fuel is circulated back to the inlet side of the pump47, as described hereinafter. These fuel injectors or nozzle units 9 areno part of the present invention. One suitable type thereof, designedfor intermittently discharging fuel into'the engine cylinders isdescribed and claimed in applicants Patent No. 2,516,828, issued July25, 1950. Another suitable type of injector or nozzle, Well known in theart, consists essentially of a taes are calibrated orifice through whicha continuous spray of fuel is injected into the air stream in the engineair induction system or manifold.

The excess fuel which flows from the injection units 9 to the returnmanifolds 39 is led to a pressure regulating device or by-pass device 84having a slidable valve 85 which controls a flow restricting orifice 87through which the excess fuel flows back to the intake side of the pump47, downstream of the orifice 82. The fuel flow through the latterorifice is thus equal to the engine fuel flow.

The valve 85 is actuated by two pressure responsive diaphragms 89 and90. By means of conduits 91 and 92 the fuel pressure upstream anddownstream of the orifice 82 is brought to bear on opposite sides of theformer diaphragm, thus applying to the valve 85 an axial load whichincreases with the engine fuel supply, in a direction to increase theeffective area of the orifice 87.

The flexible diaphragm 90, connected at its center with the valve 85,has'a cup-shaped outer portion whose periphery is secured to aco-operating cup-shaped member 101 connected with the resiliently loadedpiston 102 of a hydraulic servo motor 103 controlled by a venturi airdensity responsive bellows 104. By means of a conduit 105 and passages107 and 108 the venturi differential pressure is brought to bear onopposite sides of the diaphragm 90, thus transmitting to the valve 85 aload which increases with the venturi air flow and tends to shift thevalve in a direction to decrease the open area of the pressureregulating orifice 87. A bellows 109 connected with the cup member 101serves to define higher and lower air pressure chambers within thediaphragm housing. The cup-member 101 and the diaphragm are so designedthat as the former slides toward the latter, an increasing annular outerportion of the diaphragm is caused by the air pressure differential tocome into contact with the member 101, thereby decreasing the diaphragmarea which is effective as pressure responsive means for the actuationof the valve 85. The effective diaphragm area is thus variablyadjustable and is dependent upon the position of the piston 102.

Fluid under pressure, for example lubricating oil from the engine,continuously flows into the cylinder chamber 111 through a small flowrestricting orifice 112. This oil leaves the cylinder chamber throughanother orifice 113 formed in the piston 102 and controlled by a needlevalve 114 connected to the bellows 104. Thus the piston constantlyfollows the needle 114 at definite distance therefrom without exertingany reaction on the bellows 104; when the latter contracts, the openarea of orifice 113 increases, the oil pressure in chamber 111 drops,and the piston spring plus the differential air pressure on member 101move the piston 102 toward the bellows. Conversely, when the latterexpands, the effective area of orifice 113 decreases, and the increasingoil pressure in chamber 111 moves the piston away from the bellows.

The bellows 104 contains a definite mass of air or gas, and the wallsthereof are so highly flexible as to expand or contract within thedesigned limits under negligible load. This bellows is surrounded byinduction air in the immediate vicinity of the venturi, the air withinthe bellows thus being at the same pressure and temperature as the airflowing through the venturi, and therefore having the same density. As aresult, the volume and in turn the length of the bellows are inverselyproportional to the venturi air density.

where 6 is the venturi air density and I is the venturi" Patented Apr.21, 1959.

pressure differential. In the above formula and in the following ones Krepresents various constants dependent upon the geometrical unchangingdimensions of the metering elements and, in some of the formulae, alsoupon the fuel density.

The load P applied to the valve 85 by the diaphragm 90 is 2 P: K D 1 KEwherein D is the effective diameter of the diaphragm, that is, thediameter of the portion thereof which is not in contact with thecup-member 101.

On the other hand the fuel flow per second w through the orifice S2 isw=Ks' /z where s is the variable effective area of the orifice 82,

and i is the fuel pressure drop across the orifice. The load transmittedto the valve 85 by the diaphragm 89 is The valve 85 is subject to thelight load of an idling spring 115 adjustable by means of a threadedcap. However, when the engine operates at normal speed this spring loadis negligible with respect to the loads p and P. Furthermore, under theoppositely directed loads p and P the valve is in equilibrium.Substituting the relation p=P in the above equations we obtain thefollowing expression for the engine fuel-air ratio IT i s;g

The diaphragm 90 and the cup member 101 are so designed that as theventuri air density varies and the bellows 104 expands or contracts andshifts the cup member, the effective diameter of the diaphragm variesproportionally to the square root of the air density, thus rendering thefraction D/VE constant. The fuel-air ratio then becomes w/W=Ks, in otherwords this ratio is determined by the adjustment of the needle valve 83exclusively, irrespective of changes of altitude within the designedlimits.

The profile of the cup member 161 and diaphragm 90 may readily bedesigned to satisfy the above requirement. If the axial length of thebellows 1% when subject to standard sea level air density is L, and thecorresponding predetermined effective diameter of the diaphragm is d, athigh altitude where the venturi air density is one half of the standardsea level value the length of the bellows is 2L, and owing to thechanged position of the cup member relative to the diaphragm, theeffective diameter of the latter will have to be 0.707 d. At higheraltitude where the venturi air density is one fourth of the standard sealevel value, the length of the bellows is 4L, and the effective diameterof the diaphragm will be 0.5 d.

Manual as well as automatic control of the valve 83 may be provided toregulate the engine fuel-air ratio. Four cams are shown in the drawingfor actuating this valve. The cam 116 is manually controlled by means ofsuitable linkage means. Cam 117 is connected to a manifold air pressureresponsive bellows 118. Cam 119 is actuated in dependence upon theengine speed by a resiliently loaded diaphragm 120 responsive to thefuel pressure drop determined by an orifice 121 provided on thedischarge side of the volumetric engine-driven pump 47, and cam 122 isactuated by a bellows 123 connected with an element 124 responsive tothe manifold air temperature and preferably also responsive inpredetermined degree to the engine cylinder temperature. The number,character and arrangement of the automatic devices connected with thefuel-air ratio control valve 83 may of course be varied to suit specificcharacteristics of various types of engines.

In operation, the fuel discharged under pressure by the pump 47 is ledthrough the supply manifolds 45 to the various injectors 9; part of itis delivered to the engine, and the excess returns to the inlet port ofthe pump 47 through the return manifolds 39 and the by-pass orifice 87controlled by the valve 85. When the valve is set in its extreme leftposition, with the by-pass orifice 87 fully open, no appreciable amountof pressure is set up on the discharge side of the pump 47 or within theinjectors 9, and the latter therefore do not deliver any fuel to theengine; the fuel discharged by the pump 47 is all returned to the inletport thereof, no new fuel is admitted from the tank through the inletpipe 81, and therefore no pressure drop is set up across the restriction82 controlled by the valve 83. On the other hand, when the same valve 85is in its extreme right position, reducing to a minimum the open area ofthe orifice 87, the pressure of the fuel on the discharge side of thepump 47 and in the injectors 9 attains its maximum value, the injectors9 deliver to the engine their maximum designed fuel flow, and the flowof fuel from the tank through the restriction 82, and therefore thepressure drop across said restriction, attain their maximum value. It isthus clear that the valve 85 variably controls the pressure drop orpressure head across the restriction 82.

As already stated, the diaphragm exerts on the valve 85 a load which isa measure of engine air flow; and any variation in the venturidifferential pressure or in the pressure and/or temperature of the airsurrounding the bellows 104 actuates the valve 85 to alter the pressurehead across the restriction 82. Since any change in the speed of theengine is accompanied by a corresponding variation in engine air flow,it follows that any variation in engine speed will cause operation ofthe valve 85.

These embodiments of the invention have been shown merely for purpose ofillustration and not as a limitation of the scope of the invention. Itis therefore to be expressly understood that the invention is notlimited to the specific embodiment shown, but may be used in variousother ways, in connection with other types of prime movers, that variousmodifications may be made to suit different requirements, and that otherchanges, substitutions, additions and omissions may be made in theconstruction, arrangement and manner of operations of the parts withoutdeparting from the limits or scope of the invention as defined in thefollowing claims.

In interpreting the claims, where they are directed to less than all ofthe elements of the complete systems disclosed, they are intended tocover possible uses of the recited elements in installations which lackthe nonrecited elements.

I claim:

1. In a fuel control system for an engine having a combustion chamberand a compressor for supplying air to said combustion chamber, a fuelnozzle for discharging fuel under pressure into said combustion chamber,a conduit for conducting fuel to said nozzle, and fuel flow controlmeans in said conduit including a metering restriction, a metering valvecontrolling the area of said restriction, an independent fuel pressuredifferential responsive regulator valve controlling the metering headacross said restriction, and means responsive to a pressure generated bythe compressor and operatively connected to said metering valve forvarying the flow of fuel through said restriction as a function of saidgenerated pressure.

2. In a fuel control system for an engine having a cornbustion chamberand a compressor supplying air for combustion, a fuel nozzle fordischarging fuel under pressure into said combustion chamber, a conduitfor conducting fuel to said nozzle, and fuel flow control means in saidconduit including a metering restriction, a metering valve controllingthe area of said restriction, an independent fuel pressure differentialresponsive regulator valve controlling the metering head across saidrestriction, and means responsive to absolute pressure generated by thecompressor and operatively connected to said metering valve for varyingthe flow of fuel through said restriction as a function of said absolutepressure.

3. In a fuel control system for an engine having a combustion chamberand a compressor for supplying air to said combustion chamber, a fuelnozzle for discharging fuel under pressure into said combustion chamber,a conduit for conducting fuel to said nozzle, a fuel pump arranged topressurize the fuel in said conduit, and fuel flow control means in saidconduit including a metering restriction, a metering valve controllingthe area of said restriction, an independent fuel pressure differentialresponsive regulator mechanism controlling the metering head across saidrestriction, said mechanism including a regulator valve arranged toby-pass fuel from the high pressure side to the low pressure side ofsaid pump and means for subjecting the regulator valve to a differentialpressure varying with the metering head across said restriction, andmeans responsive to a pressure generated by the compressor andoperatively connected to said metering valve for varying the flow offuel through said 10 restriction as a function of said generatedpressure.

No references cited.

